Hybrid vehicles generally have a heat engine constituting the main power unit of the vehicle, and a supplemental power unit utilizing energy that can be stockpiled, such as electric or hydraulic energy, to optimize the operation of the heat engine and reduce its consumption.
One known type of hybrid vehicle, presented in particular by the document JP-8282324, uses a heat engine constituting the main power unit, and a hydraulic machine connected to the drive wheels of the vehicle, being able to operate as a pump to charge hydraulic pressure accumulators, or as a motor to deliver a mechanical power to these drive wheels by withdrawing energy from the accumulators.
In this way, during the braking phases one can utilize the hydraulic machine as a pump to recharge the hydraulic accumulators, recovering the kinetic energy of the vehicle. One can also utilize the hydraulic machine as a motor by withdrawing pressurized fluid from the hydraulic accumulators, and furnishing a mechanical power that is added to the power delivered by the heat engine, for the traction of the vehicle.
This utilization of stockpiled hydraulic energy makes it possible to optimize the operation of the heat engine and to reduce its consumption, as well as the polluting gas emissions. The stockpiling of hydraulic energy also makes it possible to drive in hydraulic mode alone or zero emission “ZEV” mode, the heat engine remaining halted with a vehicle not emitting any polluting gas.
The problem that arises with this type of vehicle is that the quantity of energy stockpiled is limited by the capacity of the hydraulic accumulators, which do not provide a good ratio between the quantity of energy stockpiled and the mass of these accumulators. The mileage in zero emission mode is thus slight in relation to the payload of the vehicle.